Dr. Redden's Notes
Ensuring High-Quality Radiographs of the Equine Foot
Written by R.F. (Ric) Redden, DVM
Radiographic examination of the equine foot can provide a wealth of information when performed in a methodical manner. There is no single protocol that is suitable for every case, but the same basic approach applies to every radiographic examination.
Preparation The foot should be thoroughly cleaned of all debris, including any material that may have lodged in the sulci of the frog. The shoe may need to be removed for a complete digital study; however, it can be left in place for lateral, dorsopalmar (DP), and 65-degree DP views. In fact, leaving the shoe on can provide useful information. Also, in very lame horses leaving the shoe on minimizes pain and saves time and expense. The surface of the dorsal hoof wall should be delineated from the top of the wall to the toe using a radiopaque material, such as contrast paste. To facilitate uniform views, the horse's feet should be placed on wooden blocks (one block under each foot).
Equipment and Exposure Factors Obtaining consistent, high-quality radiographs requires familiarity with the radiographic equipment. It is well worth taking the time to formulate a detailed technique chart for the x-ray machine, film-screen combination, and processing method you routinely use. Two exposures should be taken for each view. The author uses the following terminology for exposure factors: "soft" (for nonbony tissues), "medium" (for bone of moderate density), and "hard" (for dense bone). Specific exposure factors will vary with the equipment used. Soft tissue detail is essential on at least one film per view, as the nonbony tissues surrounding the distal phalanx are an integral part of all foot problems. However, it is important to establish a range of normal for different breeds and age groups.
Routine Views Accurate positioning is as important as the exposure factors used. For the lateral view, the x-ray beam is aimed 1–2 cm above the bearing surface (i.e. at the level of the apex of the distal phalanx), midway between heel and toe. The beam must be horizontal and perpendicular to the sagittal plane of the foot. The two exposures recommended for this view are soft and medium. For a lateral view of the navicular bone, the beam is centered approx. 5 cm (2 in) higher and further toward the heel (i.e. over the navicular bone). The two exposures recommended are medium and hard (using a 6:1 parallel grid). For the DP view, the horizontal beam is centered at the toe, again at the level of the apex of the distal phalanx. The two exposures recommended are soft and medium. The same exposure factors can be used for the 65-degree DP. For evaluation of the navicular bone on this view, the beam is centered over the navicular bone and a hard exposure is taken using a grid. To prevent distortion of the distal phalanx on any of these views, it is important to ensure that the cassette is in contact with the foot and the beam is perpendicular to the cassette.